The dramatic growth of portable and hand held communications equipment, such as wireless, internet access, local area network equipment, has created an enormous demand for bandwidth. With the band below 1 GHz essentially saturated, new equipment will operate between 1 and 30 GHz, and future systems already in planning operate up to 100 GHz. These high frequencies place heavy demands on existing device fabrication technologies, and in some cases will require the development of new techniques and designs.
The basic fabric of microwave devices are microstrip lines. The power loss in microstrip lines largely determines the overall Q factor of the device. Low loss increases device performance, reduces cost of the overall system, and reduces power consumption. The latter feature is especially critical for portable and hand held equipment.
Loss in microstrip lines depends to first order on the transmission efficiency of the transmission medium. This would appear to be primarily a function of the Q of the microstrip material. However, in many cases other factors dominate. For example, thin film microstrips are typically formed by sputtering onto a substrate using a buffer layer to improve adhesion between the substrate and the microstrip. The interface between the buffer layer and the microstrip is a source of significant loss, and this loss increases dramatically with frequency. In thick film microstrips, while the Q of the material is typically high, control of the microstrip edge definition is relatively poor, and thick film microstrips tend to have rough surfaces. Surface roughness and edge definition are small loss factors at low frequencies, but become very significant at high frequencies.
Polymer striplines overcome some of these deficiencies, but inexpensive, low loss polymer materials are of limited availability.
Thus there is a need in the art for new approaches to stripline manufacture. The ideal would be a process and device which captures the bulk properties of thick film striplines with the geometric control of thin film technology.